In the use of electrostatic spray guns, there is a need to know the level of voltage existing at the electrostatic electrode during operation of the spray gun. Firstly, the voltage and current are helpful in indicating that the spray gun is operating properly; and secondly, the voltage and current may indicate certain information about the details of the application of paint spray to the parts or media being sprayed.
It must be assumed that an electrostatic spray gun will be operated in an environment containing highly volatile or flammable materials, and accordingly, the possibility of explosions must always be kept in mind where there is an inclination to transmit information which would ordinarily be transmitted by electrical wiring. Presently, electrostatic spray guns are known to operate without any electrical connections whatever to external circuitry or power sources; and the only power supplied to the electrostatic spray gun is by way of high pressure air transmission wherein the air is used for spraying the paint and is also used to drive a self-contained turbine-generator within the electrostatic spray gun body, the output from such a generator being used to establish the high voltage applied to the electrostatic electrode in the spray gun.
Because of the oftentimes highly volatile and contaminated atmospheric conditions in which the spray gun operates, the spray gun is oftentimes operated by a robot and control of the spray gun is effected at a remote location, oftentimes behind explosion-proof barriers, so that the control is at some distance, such as ten to fifty feet from the actual location of the spray gun.